Solution mining of sloping strata



Sept 12, 1967 J. a. DAHMS ETAL 3,341,252

SOLUTION MINING OF' SLOPING STRATA syeoN R nMoA/ns f BY @Ak/w# SMM ATTORNEYS SePt- 12 1967 J. s. DAHMs ETAL SOLUTION MINING OF SLOPING STRATA 5 Sheets-Sheet 2 Filed April v, 1965 ....9 DOOM@ 202 ATTORNEYS United States Patent Ot SOLUTION MINING OF SLOPING STRATA James Bowen Dahms, New Martinsville, W. Va., and

Byron Priestly Edmonds, Regina Saskatchewan, Canada, assignors to Kalium Chemicals Limited, Regina,

Saskatchewan, Canada, a corporation of Canada Filed Apr. 7, 1965, Ser. No. 446,369 16 Claims. (Cl. 299-4) ABSTRACT OF THE DISCLOSURE A soluble product deposit situated adjacent a soluble non-product deposit is solution mined in the direction of the strike to minimize extraction of non-product minerals.

This invention relates to solution mining a soluble. It more particularly relates to solution mining a sloping stratum of soluble product minerals disposed adjacent soluble non-product minerals.

In a typical solution mining operation, a plurality of bore holes is established through a plur-ality of strata of varying compositions to a lower deposit of product minerals. By product mineral is meant a mineral which it is commercially desirable to extract. These minerals are extractable with suitable solvents typically with aqueous media including mineral acids, steam, salt solution, e.g., solutions of NaCl and/or KCl, substantially pure water, etc. The bore holes are normally provided with suitable casings which communicate with a cavity in the mineable (product) deposit. Usually a plurality of solution mining cavities are operated concurrently to produce suflicient eilluent to feed an aboveground recovery operation. As extraction of the mineral deposit proceeds, the cavities enlarge in both the vertical and horizontal directions.

Typical of the deposits extracted by solution mining techniques are sedimentary deposits, e.g., evaporites of sodium chloride, potassium chloride, or mixtures thereof. These deposits often exist as a plurality. of sloping strata. These strata slope substantially in the direction of the dip, i.e., normal to the strike thereof. Strata of product minerals are frequently disposed adjacent extractable nonproduct minerals. Because of the tendency of a solution mining cavity to maintain a substantially level roof, the maximum dimensions of a cavity in the direction of the dip lying substantially wholly within a sloping product stratum are severely limited. As used herein and in the claims, the direction of the strike is considered to be a course parallel to the strike. The direction of the dip is a horizontal course normal to the direction of the strike.

In a typical solution mining operation, the tendency is for the cavity roof to extract relatively rapidly in the vertical direction. Thus, it is usually desirable to feed along with the solvent to the cavity an immiscible, nonsolvent which is inert to the materials being extracted and the solvent. This inert non-solvent material, typically hydrocarbon oil is lighter than the solution in the cavity. Thus, it forms a protective layer adjacent the cavity roof thereby encouraging horizontal expansion of the cavity. In this fashion, two or more cavities are often brought into communication. Other employable non-solvents include inert gases such as air. lnert liquids are preferred.

When the roof of one solution mining cavity communicates with a second cavity disposed at a higher level than the rst cavity, the inert non-solvent pad at the roof of the lower cavity tends to ilow to the uppermost cavity. The roof of the lowermost cavity is then unprotected against further vertical extraction. Usually, the roof of the lower cavity eventually rises to about the level of the roof of the uppermost communicating cavity. Such communication in the sloping product strata hereinbefore described 3,341,252 Patented Sept. 12, 1967 is often undesirable. Where the two cavities are spaced in the direction of the dip, the usual result of communication of the two cavities is to extract a large amount of non-product minerals as the roof of the lower cavity rises to the level of the roof of the upper cavity. The dissolving capacity of the solvent is thereby wasted. The economics of a subsequent recovery operation are adversely aected by undue quantities of non-product materials in the effluent from the solution mining cavities.

The instant invention provides a new technique whereby undesirable communication of cavities in the direction of the dip is provided against. According to the instant invention, a plurality of bore holes spaced in both the directions of the dip and the strike are provided to communicate with a product stratum. Bore holes spaced in the direction of the strike are brought into communication by developing cavities to communicate therewith. Communication between bore holes spaced in the direction of the dip is avoided. By properly directing solvent ilow into the cavity, lateral expansion of the cavity is encouraged in the direction of the strike. Lateral expansion in the direction of the dip is thereby minimized and communication between cavities in the direction of the dip is guarded against. In this way, cavities of substantial dimensions are economical to operate. The cavities being confined to the product stratum, extraction of undue quantities of non-product minerals is avoided.

This invention is more readily understood with reference to the accompanying drawings. FIGURE l shows in plan view the orientation of cavities taught by the instant invention. FIGURES 2 and 3 are sectional views of a deposit comprising sloping strata as viewed across the dip and the strike, respectively. FIGURE 4 shows the resultant cavity formed by communication of the cavities of FIGURE 2. FIGURE 5 illustrates a typical device used to direct influent in a desired direction.

Referring to the drawings, a plurality of bore holes communicating with the product stratum are spaced in the directions of the strike and dip. Cavity 8 is located uphill of cavity 18 in the direction of the dip of the mineral deposit. Cavity 28 is spaced in the direction of the strike from cavity 8. Oil pads 6, 16 and 26 insulate the roofs of the respective cavities from extraction. Inlluent bore holes 1, 11 and 21 are spaced in the direction of the strike from eluent bore holes 2, 12 and 22, respectively. FIGURES 2 and 3 illustrate the comparatively larger development of the cavities desired in the direction of the strike than in the direction of the dip.

In practice, solution mining cavities are developed at the bases of each of several bore holes in accordance with well known techniques. The cavities are then encouraged to develop in the direction of the strike until one or more cavities communicate. The deposit is then solution mined in accordance with recognized techniques whereby one or more bore holes accommodate feed or influent conduits. Eilluent is Withdrawn from the cavities through conduits substantially removed from the influent conduits. The effluent conduits are located in the direction of the strike from the influent conduits. Communication between cavities in the direction of the dip is discouraged. In this fashion, circulation of cavity fluid maximizes in the direction of the strike thereby tending to produce elongated cavities as shown in FIGURE 3.

Cavity development in the desired direction may be further encouraged by directing the solvent influent at its point of introduction in the direction of the strike. Solvent is conveniently so directed by means of a suitably oriented nozzle or orifice disposed at the terminus of the influent casing. Several devices for directing solvent feed llow are disclosed, for example, in U.S. Patent 2,251,916. FIGURE 5 illustrates a typical nozzle 9 employable in the practice of this invention. Other means of directing solvent flow and providing for cavity expansion in the desired direction are, of course, within contemplation. For example, after two cavities are brought into communication the casting most remote in the direction of the strike from the influent casing is employed as the efiiuent conduit. It has been found that once communication is established, maximizing the distance between the infiuent and efiiuent conduits in the direction of the strike discourages cavity growth in the direction of the dip.

For the practice of this invention, it has been found desirable to space the initial bore holes in the direction of the dip at least about 2, preferably about 5 or more times the spacing of the bore holes in the direction of the strike. Spacing distances are measured along the horizontal at the bottom ends of the bore holes or extensions thereof. By extension is meant conduits, casings or pipes internal to but extending beyond the ends of the bore holes. The preferred spacing of bore holes in the direction of the dip is determined by the thickness and angle ofthe product stratum. This spacing should be sufficient lthat a cavity which extracts substantially the entire stratum along the strike remains out of communication with cavities adjacent thereto in the direction of the dip. Thus, for example, a stratum sloping at about 1/2 degree from horizontal and about 50 feet thick is advantageously mined with bore holes spaced at least about 200 to about 1,000 or more feet apart in the direction of the dip. After communication has been established between bore holes in the direction of the strike, it is often possible to operate the resulting cavity through a pair of bore holes spaced from about 2,000 to about 4,000 or more feet in the direction of the strike without undue extraction in the direction 0f the dip.

The significant feature of the instant invention is that cavity development is encouraged along the direction of strike and discouraged in the direction of the dip, thereby avoiding undue dissolution of non-product minerals. The effect of allowing two cavities to communicate in the direction of the dip is illustrated by FIGURE 4. Thus, if cavity 18 is allowed to communicate with cavity 8, for example, the resulting communicating cavity tends to enlarge vertically until the roof of cavity 18 attains the level of the roof of cavity 8. It is seen from the drawing that most of the material extracted thereby as a result of the communication of these cavities is non-product.

This invention is particularly useful in solution mining deposits such as a sloping potassium chloride-rich stratum disposed intermediate to two KCl-lean NaCl-rich strata. It is equally useful in solution mining any stratum of product minerals disposed adjacent non-product soluble materials. This invention also has application where the product deposit is disposed adjacent non-extractable material in the vicinity of either its upper or lower interface. The benefits of this invention are most noteworthy where the product deposit is adjacently disposed along its upper surface to non-product soluble materials.

Although this invention has been described with particular reference to certain specific embodiments thereof, it is not intended thereby to limit the scope of the invention except insofar as specific details are recited in the appended claims.

1. In solution mining a sloping subterranean stratum of soluble product minerals disposed adjacent soluble nonproduct minerals, the improvement which comprises providing in communication with the product stratum a plurality of bore holes spaced in the directions of the strike and the dip thereof, avoiding communication between bore holes in the direction of the dip by preferentially establishing communication between bore holes in the direction of the strike, feeding solvent through a first bore hole to extract product minerals and withdrawing efiiuent bearing product minerals through a second bore hole communicating with the first bore hole and spaced from said first bore hole in the direction of the strike thereby to develop a solution mining cavity in the direction of the strike in preference to the direction of the dip thereby minimizing extraction of non-product minerals.

2. The improvement of claim 1 wherein a plurality of pairs of bore holes communicate in the direction of the strike.

3. The improvement of claim 1 wherein solvent is directed at the point of introduction to the cavity towards the cavity walls in the direction of the strike.

4. In solution mining a sloping subterranean deposit rich in potassium chloride disposed adjacent soluble deposits lean in potassium chloride, the improvement which comprises providing in communication with the potassium chloride-rich deposit a plurality of bore holes spaced in the directions of the strike and dip thereof, avoiding communication between bore holes in the direction of the dip by preferentially establishing communication between pluralities of said bore holes in the direction of the strike feeding solvent through a first bore hole to extract potassium chloride and withdrawing potassium chloridecontaining efliuent through a second bore hole communieating with the first bore hole and spaced from said first bore hole in the direction of the strike thereby to develop a subterranean solution mining cavity in the direction of the strike in preference to the direction of the dip, said cavity being located substantially in the potassium chloride-rich stratum, thereby minimizing extraction of potassium chloride-lean material.

5. The improvement of claim 4 wherein the potassium chloride-rich deposit is located adjacent and between deposits relatively lean in potassium chloride but rich in sodium chloride.

6. In solution mining a sloping subterranean stratum of soluble product minerals disposed adjacent soluble nonproduct minerals, the improvement which comprises proyiding in communication with the product stratum a plurality of bore holes spaced in the directions of the strike and the dip thereof, the distance between the bore holes in the direction of the dip measured horizontally being at least two times the distance between bore holes in the direction of the strike, establishing communication between bore holes in the direction of the strike while avoiding such communication in the direction of the dip, feeding solvent through a first bore hole to extract product minerals and withdrawing efiiuent bearing product minerals through a second bore hole communicating with the first bore hole in the direction of the strike to develop a solution mining cavity in the direction of the strike in preference to the direction of the dip thereby minimizing extraction of non-product minerals.

'7. In solution mining sloping subterranean deposits rich in potassium chloride disposed adjacent soluble deposits lean in potassium chloride, the improvement which comprises providing in communication with a potassium chloride-rich deposit a plurality of bore holes spaced in the direction of the strike and dip thereof, said bore holes being spaced substantially further apart in the direction of the dip than in the direction of the strike, establishing communication between pluralities of said bore holes in the direction of the strike and avoiding communication between bore holes in the direction of the dip, feeding solvent through a first bore hole to extract potassium chloride and withdrawing potassium chloride-containing effluent through a second bore hole communicating with the first bore hole in the direction of the strike to develop a subterranean solution mining cavity in the direction of the strike in preference to the direction of the dip, said cavity being located substantially in the potassium chloride-rich stratum, thereby minimizing extraction of potassium chloride-lean material.

8. The improvement of claim 7 wherein the bore holes are spaced in the direction of the dip at least two times their spacing in the direction of the strike.

9. A solution mining system comprising a plurality of sets of bore holes each of which sets communicates with a separate solution mining cavity in contact with an extractable product deposit situated adjacent and below an extractable non-product deposit, the bore holes in each said set being spaced in the direction of the strike and said sets being spaced in the direction of the dip.

10. The system of claim 9 wherein each set of bore holes consists of two bore holes.

11. The system of claim 9 wherein the product deposit is a KCl-rich deposit.

12. The system of claim 11 wherein the non-product deposit is a KCl-lean, NaCl-rich deposit.

13. The system of claim 9 wherein the product deposit is situated adjacent and above an extractable non-product deposit.

14. The system of Claim 13 wherein the product deposit is a. KCl-rich deposit and the adjacent non-product deposits are NaCl-rich, KCl-lean deposits.

6 15. The system of claim 14 wherein each set of bore holes consists of two bore holes.

16. The system of claim 14 wherein the solution mining cavities are -located substantially completely within the KCl-rich deposit..

References Cited UNITED STATES PATENTS 1,960,932 5/1934 Tracy 2994 2,009,534 7/ 1935 Trump 299-5 2,822,158 2/1958 Brinton 299-4 2,979,3 17 4/ 1961 Bays 299-4 ERNEST R. PURSER, Primary Examiner. 

1. IN SOLUTION MINING A SLOPING SUBTERRANEAN STRATUM OF SOLUBLE PRODUCT MINERALS DISPOSED ADJACENT SOLUBLE NONPRODUCT MINERALS, THE IMPROVEMENT WHICH COMPRISES PROVIDING IN COMMUNICATION WITH THE PRODUCT STRATUM A PLURALITY OF BORE HOLES SPACED IN THE DIRECTIONS OF THE STRIKE AND THE DIP THEREOF, AVOIDING COMMUNICATION BETWEEN BORE HOLES IN THE DIRECTION OF THE DIP BY PREFERENTIALLY ESTABLISHING COMMUNICATION BETWEEN BORE HOLES IN THE DIRECTION OF THE STRIKE, FEEDING SOLVENT THROUGH A FIRST BORE HOLE TO EXTRACT PRODUCT MINERALS AND WITHDRAWING EFFLUENT BEARING PRODUCT MINERALS THROUGH A SECOND BORE HOLE COMMUNICATING WITH THE FIRST BORE HOLE AND SPACED FROM SAID FIRST HOLE IN THE DIRECTION OF THE STRIKE THEREBY TO DEVELOP A SOLUTION MINING CAVITY IN THE DIRECTION OF THE STRIKE IN PREFERENCE TO THE DIRECTION OF THE DIP THEREBY MINIMIZING EXTRACTION OF NON-PRODUCT MINERALS. 